MECHANISM OF ACTION AND POTENTIAL ENVIRONMENTAL BENEFITS FROM THE USEOF FEED ENZYMES

The efficiency of utilisation of wheat, oats, barley and rye by poultr y is often limited by the presence of antinutritional factors (ANFs). Such ANFs are commonly referred to as non-starch polysaccharides, clas sified as arabinoxylans and beta-glucans. The arabinoxylans, which con sist of a linear backbone of xylose substituted with arabinose, are re sponsible for the bulk of the problems encountered in birds fed wheat or rye based diets, whilst the beta-glucans, a linear polymer of gluco se with kinks in its structure, are responsible in oats and barley. Ho wever it is only the high molecular weight arabinoxylans and beta-gluc ans that are responsible. Both beta-glucans and arabinoxylans exert th eir negative effects on digestion by creation of very large entangleme nts which result in an elevation of viscosity of the small intestine. Such an elevation results in a reduction in the rate of digestion and absorption of nutrients, an elevation of microbial activity in the int estine, a reduction in feed intake and increased litter moisture. The application of relevant and effect xylanases and beta-glucanases can a lleviate these problems by reducing the molecular size of the target s ubstrate, which in turn reduces the viscosity of the intestine and hen ce enables more rapid digestion. It is unlikely that exogenous enzymes reduce the beta-glucans and arabinoxyIans to their constituent sugars since relatively few catalytic events are necessary to reduce the mol ecular size and hence viscosity of these complexes. A more detailed un derstanding of the structure of these viscous complexes as they appear in the intestine will enable the design of more specific enzymes for poultry feeds.